1. Field of the Invention
The present invention relates to an antenna, and in particular to an antenna which is capable of operating in two distinct frequency bands.
2. Description of the Prior Art
In recent years, planar inverted-F antennas (PIFA) have become increasingly popular. U.S. Pat. No. 5,926,139 issued to Korich on Jul. 20, 1999 discloses a conventional antenna. The conventional antenna comprises a planar dielectric substrate having opposite upper and lower major surfaces. A ground plane and a radiating element are respectively disposed on opposite major surfaces of the substrate. The radiating element comprises a first radiating portion and a second radiating portion. The first radiating portion is sized to function as a first PIFA operating in a first frequency band. The second radiating portion is sized to function as a second PIFA operating in a second frequency band. Therefore, the conventional antenna is capable of operating in two frequency bands. However, because the radiating element and the ground plane are respectively disposed on the opposite major surfaces of the substrate, the antenna has to form a grounding pin extending through the dielectric substrate to interconnect the ground plane and the radiating element, and a feed pin extending through the ground plane and the substrate to couple the radiating element to a transceiver circuitry. The conventional antenna has, therefore, a complex structure. Furthermore, the conventional antenna has a narrow bandwidth.
Hence, an improved antenna is desired to overcome the above-mentioned shortcomings of existing antennas.
A main object of the present invention is to provide a dual band antenna having a simple structure and having a wide bandwidth.
A dual band antenna in accordance with the present invention is mounted in an electronic device for transmitting or receiving signals. The dual band antenna comprises a planar conductive element and a feeder cable electrically connecting to the conductive element. The conductive element includes a first radiating strip, a second radiating strip, a ground portion, and a connection strip. The connection strip interconnects the first and the second radiating strips with the ground portion. The first radiating strip and the connection strip are configured and sized to function as a first planar inverted-F antenna (PIFA) operating in a higher frequency band. The second radiating strip and the connection strip are configured and sized to function as a second PIFA operating in a lower frequency band. Because the first and the second radiating strips, the ground portion and the connection strip are all disposed in the same plane, the dual band antenna has a simple structure and has a wide bandwidth in the higher frequency band.
Other objects, advantages and novel features of the invention will become more apparent from the following detailed description of a preferred embodiment when taken in conjunction with the accompanying drawings.